As more and more various home eNBs, pico cells, relay nodes and other Local evolved NodeBs (LeNBs) are deployed, the traditional network architecture in which Macro eNBs (MeNBs) are predominant will evolve gradually into a network architecture in which more types of eNBs coexist to provide layered network coverage. In order to improve correlation performance in the network architecture in which the various types of eNBs coexist, a network architecture in which a plurality of eNBs cooperate/are aggregated with each other has been proposed. In this architecture, a part of Radio Bearers (RBs) of a User Equipment (UE) are active in a macro cell managed by the MeNB, where this part of the RBs include control plane bearers (i.e., Signaling Radio Bearers (SRBs)) and user plane bearers (i.e., Data Radio Bearers (DRBs)), and the other part of the bearers of the same UE (including SRBs and DRBs) are active in a small/local cell managed by the LeNB. If there is a Radio Link Failure (RLF) of the UE occurring in the cell managed by the LeNB, then the UE may be controlled by the MeNB to reestablish a bearer with the LeNB/MeNB, and also the UE may make an RLF report. However, the reason for the RLF of the UE occurring in the small cell may be that a bearer splitting parameter controlled by the MeNB/LeNB is set inappropriately.
There is the following layered network deployment scenario including a macro eNB and local eNBs:
In the layered network coverage environment as illustrated in FIG. 1, the macro eNB can provide underlying coverage, and the local eNB can provide hotspot coverage; and there is a high-speed data/signaling interface, i.e., an M-L interface (a wired or radio interface) between the macro eNB and the local eNB, and the UE can operate while being served by bath the macro eNB and the local eNB. If the UE connected to the macro eNB enters a coverage area of a cell corresponding to the local eNB, then the MeNB can transfer a part or all of data/signaling of the UE to the local eNB taking into account signal strengths, load balancing, etc., so that the UR can be served by the local eNB, thus enabling the UE to operate over resources of both the macro eNB and the local eNB, and inter-eNB aggregation. In this scenario, a plurality of Radio Bearers (RBs) of the UE can be carried respectively in a cell controlled by the macro eNB (i.e., a macro cell) and a cell controlled by the local eNB (i.e., a local/small cell), where the RBs split to the LeNB can include Data Radio Bearers (DRBs) and/or Signaling Radio Bearers (SRBs).
The eNB detects an RLF generally in the following two approaches. In the first approach, the eNB determines whether there is an RLF of the UE occurring in some cell, according to RLF information reported by the UE; and in the second approach, the eNB itself determines whether there is an RLF of the UE occurring in some cell.
In the first approach, the UE determines that an RLF is detected, and subsequently reports it to the eNB, upon detecting that any one of the following situations occurs:
The timer T310 expires;
A random access failure indicator at Multiple Access Channel (MAC) layer is received; and
An indicator at Radio Link Control (RLC) layer that the maximum number of retransmissions is reached is received.
At this time if security of an access stratum is not activated, then the UE may release it Radio Resource Control (RRC) connection and enter the RRC_IDLE state; otherwise, the UE may initiate an RRC Connection Reestablish procedure.
In the second approach, the eNB itself can determine whether there is an RLF of the UE occurring in some cell, for example, when some timer expires, or according to the maximum number of retransmissions of some data packet, etc.
If there is an RLF of the UE occurring, then the UE makes an RLF report after the UE establishes/reestablishes an RRC connection. The UE makes the RLF report as follows: the UE reports an RLF report availability indicator; the eNB transmits an RLF report request in response to the indicator of the UE; and the UE makes its RLF report to the eNB in response to the RLF report request transmitted by the eNB. The UE reports the RLF report availability indicator generally by carrying it in other uplink control signaling including:
RRC Connection Reconfiguration Complete;
RRC Connection Reestablishment Complete; and
RRC Connection Setup Complete.
The UE distinguishes the following two types of the occurring connection failure reported in the RLF report from each other and signals explicit indicators thereof to the eNB:
A handover Failure (HOF) which is a connection failure occurring in a handover procedure; and
An RLF which is a connection failure occurring in a non-handover procedure.
There are the following scenarios in question where the RLF report is made and processed without splitting bearers;
The RLF report is processed generally by handling the RLF/HOF of the UE in respective scenarios. The following three handovers are defined in the intra-LTE (LTE stands for Long Term Evolution):
A too late handover where after the UE has stayed in the cell for a very long period of time, the RLF occurs; and the UE attempts on reestablishing a radio link connection in a different cell;
A too early handover where the RLF occurs in a very short period of time after the handover from a source cell to a destination cell occurs, or the HOF occurs in the handover procedure; and the UE attempts on reestablishing a radio link connection in the source cell; and
A handover to wrong cell where the RLF occurs in a very short period of time after the handover from a source cell to a destination cell occurs, or the HOF occurs in the handover procedure; and the UE attempts on reestablishing a radio link connection in a cell other than the source and destination cells; and
These three handovers are detected as follow:
A failure after an attempt on reestablishing an RRC connection is detected:
For the too late handover, if the UE attempts on reestablishing a connection in a cell served by the eNB_B, and indicates the last serving cell is served by the eNB_A instead of the eNB_B, then the eNB-B reports this event to the eNB_A in an RLF indication procedure. The eNB_A can determine from information in an RLF Indication message whether there is a failure occurring in the serving cell.
For the too early handover, if the destination cell where the RLF occurs is served by the eNB_B instead of the eNB_A, and the UE reestablishes a connection with the eNB_A, and makes the RLF report, after the connection failure; if the eNB_B receives an RLF Indication message from the eNB_A, and if the eNB_B has transmitted a UE Context Release message to the eNB_A, and the UE has been handed-over successfully for a period of time which is in a Tstore_UE_cntxt or there is a handover of the UE prepared at the eNB_B side, then the eNB_B transmits a Handover Report message to the eNB_A to indicate the too early handover event.
For the handover to wrong cell, if the destination cell where the RLF occurs is served by the eNB_B instead of the eNB_A (controlling the source cell), and the UE reestablishes a connection with the eNB_C, and makes the RLF report, after the connection failure; if the eNB_B receives an RLF indication message from the eNB_C, and if the eNB_B has transmitted a UE Context Release message to the eNB_A, and the UE has been handed-over successfully for a period of time in a Tstore_UE_cntxt or there is a handover of the UE prepared at the eNB_B side, then the eNB_B transmits a Handover Report message to the eNB_A, to indicate the handover to wrong cell event. This procedure will also apply in the case that the eNB_A and the eNB_C are the same eNB. In the case that the eNB_B and the eNB_C are the same eNB, the RLF Indication message is transmitted within the eNB.
If the handover failure occurs in a handover procedure initiated from a cell of the eNB_A, and the UE attempts on reestablishing a connection with a cell of the eNB_C, then the eNB_C can transmit an RLF indication message to the eNB_A.
A failure after the RRC connection is established is detected:
For the too late handover, the UE has not been recently handed-over before the connection failure, for example, the UE has not reported temporal information, or the reported temporal information is above a configured threshold, e.g., Tstore_UE_cnxt.
For the too early handover, the UE has been recently handed-over before the connection failure, for example, the UE reports temporal information below a configured threshold, e.g., Tstore_UE_cnxt, and initially attempts on reestablishing a connection in a cell which initiates the last handover and serves the UE.
For the handover to wrong cell, the UE has been recently handed-over before the connection failure, for example, the UE reports temporal information below a configured threshold, e.g., Tstore_UE_cnxt, and initially attempts on reestablishing a connection in a cell which is neither a cell which initiates the last handover and serves the UE, nor a cell serving the UE when the RLF occurs or a cell to which the handover is initiated.
For the too early handover or the handover to wrong cell, the eNB receiving the RLF Indication message transmits a Handover Report message to the eNB controlling the cell in which the failure occurs due to mobility configuration. From the perspective of the network side, the detection of a failure after the RRC connection is established is not significantly different from the detection of a failure after the RRC connection is reestablished.
A connection failure occurs under bearer splitting:
Firstly in the scenario in question where there is a connection failure under bearer splitting, if there is a connection failure of the UE occurring in the macro cell in the bearer splitting scenario, any connection of the UE in a non-standalone local cell (the UE can not operate in a standalone mode in this type of cell but can only operate under the control of the macro cell) may fail. The connection failure arises primarily due to inappropriate setting of mobility parameters between the MeNBs, and can be handled by the network using the same approach as the detection of a failure after an attempt on reestablishing an RRC connection. A connection of the UE in a standalone local cell (the UE can operate in a standalone mode in this type of cell) can still operate, and the UE only needs to reestablish a related bearer on the LeNB, and alike the connection failure also arises primarily due to inappropriate setting of mobility parameters between the MeNBs, and can also be handled by the network side using the same approach as the detection of a failure after an attempt on reestablishing RRC connection.
Thus a bearer splitting scenario to be taken into special account is a scenario in question where the mobility related parameter is inappropriately set between the MeNB and the LeNB, i.e., a scenario where there is no connection failure of a bearer occurring on the macro cell, but there is a connection failure occurring on the local cell. There may be the following scenarios where there is a connection failure of a bearer occurring on the local/small cell:
In a first scenario, there is a bearer splitting failure without macro cell handover. Since this bearer splitting is generally bearer splitting under the circumstance that the UE and the LeNB are controlled by the MeNB, the bearer splitting failure is primarily due to inappropriate setting of the mobility parameter by the current MeNB. In this case, the RLF report made by the UE is generally made to the current MeNB or the LeNB controlled by the current MeNB.
The following splitting instances may tend to occur:
1.1 RB split too early;
1.2 RB split too late; and
1.3 RB split to wrong cell.
In a second scenario, there is a bearer splitting failure with a macro cell handover (the macro cell handover procedure and the small cell bearer splitting procedure of the UE are performed concurrently in the macro cell handover procedure). Since this bearer splitting is generally bearer splitting under the circumstance that the UE and the LeNB are controlled by the source MeNB and the destination MeNB, the bearer splitting failure is primarily due to inappropriate setting of the mobility parameter by the source MeNB. In this case, the RLF report made by the UE is generally made to the destination MeNB or the LeNB controlled by the destination MeNB.
Likewise, the splitting instances in the first scenario may also occur:
1.1 RB split too early;
1.2 RB split too late; and
1.3 RB split to wrong cell.
Secondly if there is an RLF occurring related to bearer splitting, then the UE makes an RLF report to the network side. As distinguished from the types of connection establishment failures, i.e., the HOF and the RLF, indicated previously in the RLF report, the connection of the UE on the macro cell in the bearer splitting scenario may be kept active, while there is only a radio link failure of the split bearer (the bearer on the local/small cell) occurring. Thus in order to better assist the network side in handling different types of connection failures, the LIE needs to distinguish the bearer splitting connection failure occurring on the local cell in this bearer splitting situation from the other types of connection failures when making the RLF report, to thereby make it more convenient for the network side to handle the connection failure pertinently and set a more reasonable mobility parameter related to bearer splitting.
Thirdly the network side processes the received RLF report made by the UE. The network side needs to be able to identify reasonably and treat differently the scenarios above in question.
As can be apparent, the bearer splitting scenario has not been taken into account in the improvement solution of the network to the connection failure as specified in the existing protocol so that there are absent a solution to cooperation between the network nodes and a solution to cooperation between the network and the UE, so the network nodes can not set the parameter related to bearer splitting by configuring and optimizing themselves according to the RLF report made by the UE.